1. Field of the Invention
The present invention relates to a single phase DC brushless motor, and in particular relates to a single phase DC brushless motor controller and method for controlling the rotation speed and direction of the single phase DC brushless motor.
2. Description of the Related Art
Compared with brush motors, brushless motors can commutate (reverse the rotation direction) without brushes and thus have better structural reliability and rotation efficiency, consume less power and make less noise. DC brushless motors usually have sizes smaller than AC brushless motors and are widely used in various electronic devices such as heat dissipating fans.
FIG. 1 is a schematic diagram of a conventional single phase DC brushless motor. The DC brushless motor 100 includes a rotator 110 and a stator 120, where the rotator 120 can rotate in relation to the stator 110. The rotator 110 has a plurality of magnetic poles (four poles in FIG. 1). Each of magnetic poles may be a permanent magnet, and has a magnetic field opposite to its adjacent magnetic poles (N pole or S pole). The stator 120 has the same number of magnetic poles as the rotator 110, and the magnetic poles of the stator 120 are respectively disposed on laminations (there are four laminations 121˜124 on the stator 120 in FIG. 1). However, different from the permanent magnet of the rotator 110, the magnetic field of the magnetic poles of the stator 120 are created by the coils winded around the magnetic poles, where the winding style of the coils may be radial or axial.
In order to prevent the brushless motor from starting at a commutating dead angle, each lamination (121, 122, 123 or 124) of the stator 120 has two wings 121 (as shown in FIG. 1) which have different sizes and are spaced from the rotator 110 with gaps of different sizes. In FIG. 1, when the lamination 121 is excited to be an N pole, which repels the magnetic field of the part of the rotator 110 which is facing the lamination 121, the two unbalanced wings of the lamination 121 will generate two different repelling forces in relation to the rotator 110 and rotate the rotator 110 clockwise. However, due to the commutating dead angle, reversing the rotation direction of the single phase DC brushless motor is not possible. Therefore, the single phase DC brushless motor of the prior art can only rotate in one direction.
Uni-directional rotation limits the use of the single phase DC brushless motor. To improve the ability of the single phase DC brushless motor, a motor controller which makes the motor of the prior art rotate bi-directionally is needed.